insulator (SOI) wafer. The device is based on cascaded grating-assisted contra-directional
couplers (GACDCs). It also involves the use of a subwavelength grating (SWG) structure. By
heating one of the heaters on GACDCs, a bandwidth tunability of∼ 6 nm is achieved. Owing
to the benefit of having a large coupling coefficient between SWG and strip waveguides, the
length of the coupling region is only 100 µm. Moreover, the combination of the curved SWG …